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2.3.7 Reinforcement Rules
All standards contain regulations for plate structures regarding size and direction of the reinforcement to be used. For this purpose, the standard classifies the plate structures into certain structural elements. For example, EN 1992-1-1 distinguishes the following elements of structures:
- plate (slab)
- wall (diaphragm)
- deep beam
The following graphic illustrates the relation between the user-defined Type of Model, the model for the design, and the structural element type according to the standard, which is used to determine the size and direction of the minimum or maximum reinforcement.
If 3D (see Figure 2.1) is selected as the type of model, the structural component is always designed as a shell – independent of whether both axial forces and moments occur in portions of the structural component, or if there is only one of these internal forces. A type of model defined as 2D - XY (uz/φx/φy) is always designed as a plate while the types 2D - XZ (ux/uy/φy) and 2D - XY (ux/uy/φz) are designed as walls.
After selecting the structural element type, the rules of the respective standard are automatically used in the determination of the required reinforcement. We will now briefly look at these rules for EN 1992-1-1. The standard distinguishes between solid plates, walls, and deep beams.
For solid plates, EN 1992-1-1 specifies the following:
- Clause 184.108.40.206 (1):
The minimum area of the longitudinal tension reinforcement should not be taken as less than As,min.
- Clause 220.127.116.11 (3):
The cross-sectional area of the tension or compression reinforcement may generally not exceed As,max outside lap locations. The recommended value is 0.04 Ac.
According to DIN EN 1992-1-1/NA:2010, the sum of the tension and compression reinforcement may not exceed As,max = 0.08 ⋅ Ac. This is also true for the lap locations.
For walls, EN 1992-1-1 specifies the following:
- Clause 9.6.2 (1): The area of the vertical reinforcement should lie between As,vmin and As,vmax. The recommended values are As,vmin = 0.002 ⋅ Ac and As,vmax = 0.04 ⋅ Ac outside lap locations.
- DIN EN 1992-1-1/NA:2010 specifies
- generally: As,vmin = 0.15 ∣ NEd ∣ ÷ fyd ≥ 0.0015 ⋅ Ac
- As,vmax = 0.04 ⋅ Ac (this value may be doubled at laps)
- The reinforcement content should be equal at both wall faces.
- Clause 9.6.3 (1):
A horizontal reinforcement running parallel to the faces of the wall (and to the free edges) should be provided at the outer face.
Generally, it should not be less than As,hmin.
The recommended value is the greater value determined from 25 % of the vertical reinforcement and 0.001 ⋅ Ac.
DIN EN 1992-1-1/NA:2010 specifies
- generally: As,hmin = 0.20 ⋅ As,v
- The diameter of the horizontal reinforcement should not be less than one quarter of the diameter of the perpendicular members.
According to EN 1992-1-1, clause 5.3.1 (3), a beam is considered to be a deep beam if the span is less than three times the cross-section depth. In this case, the following applies:
- Clause 9.7 (1): Deep beams should normally be provided with an orthogonal reinforcement mesh near each face, with a minimum area of As,dbmin. The recommended value is 0.001 ⋅ Ac but not less than 150 mm2 in each face and each direction.
DIN EN 1992-1-1/NA:2010 specifies
- As,dbmin = - 0.075% of Ac ≥ 150 mm2/m
In addition to the normative requirements (that cannot be modified) of reinforcement detailing, user-defined rules can be specified. These minimum reinforcements can be specified in the Reinforcement Ratios tab of the 1.4 Reinforcement window.
If we specify a minimum secondary reinforcement of 20 % of the greatest longitudinal reinforcement to be used, for example, the [Calculation] first determines the maximum longitudinal reinforcement. In the results windows, this is shown as Required Reinforcement.
We can check the minimum secondary reinforcement by clicking the [Design Details] button.
In the example above, the Reinforcement as Secondary Reinforcement into Direction 2 is 20 % of the reinforcement provided in the reinforcement direction 1 (here the main direction): 7.76 cm2/m ∙ 0.2 = 1.55 cm2/m. Since this value is greater than the Governing longitudinal reinforcement into direction 2 of 1.35 cm2/m, the secondary reinforcement is governing.